How to load the map for multiple robot navigation?

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I have followed the steps in answer for this question to setup multiple robot navigation. Everything is working well except when i launch the navigation the map is not loaded and getting the below error. I have remapped map to /map but still the target frame seems to be map, how is this possible.

[WARN] [1520794132.318544579, 556.425000000]: Timed out waiting for transform from robot2_tf/base_link to map to become available before running costmap, tf error: canTransform: target_frame map does not exist.. canTransform returned after 0.1 timeout was 0.1. 
[ WARN] [1520794132.400360318, 556.479000000]: Request for map failed; trying again...

So, how to load the map for multiple robots navigation and make them share the map.

My launch files are as follows:

Navigation of robots launch:

<launch>
  <include file="$(find gazebo_ros)/launch/empty_world.launch">
 </include>

  <!-- include our robots -->
  <include file="$(find robot_description)/launch/myrobots.launch"/>

  Run the map server 
  <node name="map_server" pkg="map_server" type="map_server" args="$(find robot_description)/maps/map.yaml" respawn="false" >
    <param name="frame_id" value="/map" />
  </node>

  <group ns="robot1">
    <param name="tf_prefix" value="robot1_tf" />
    <param name="amcl/initial_pose_x" value="1" />
    <param name="amcl/initial_pose_y" value="1" />
    <include file="$(find robot_description)/launch/move_base.launch" />
  </group>

  <group ns="robot2">
    <param name="tf_prefix" value="robot2_tf" />
    <param name="amcl/initial_pose_x" value="1" />
    <param name="amcl/initial_pose_y" value="-1" />
    <include file="$(find robot_description)/launch/move_base.launch" />
  </group>

</launch>

multiple robots launch:

<launch>
  <!-- No namespace here as we will share this description. 
       Access with slash at the beginning -->
<param name="robot_description" textfile="$(find robot_description)/urdf/myrobot.urdf" /> 

  <!-- BEGIN ROBOT 1-->
  <group ns="robot1">
    <param name="tf_prefix" value="robot1_tf" />
    <include file="$(find robot_description)/launch/one_robot.launch" >
      <arg name="init_pose" value="-x 1 -y 1 -z 0" />
      <arg name="robot_name"  value="Robot1" />
    </include>
  </group>

  <!-- BEGIN ROBOT 2-->
  <group ns="robot2">
    <param name="tf_prefix" value="robot2_tf" />
    <include file="$(find robot_description)/launch/one_robot.launch" >
      <arg name="init_pose" value="-x 1 -y -1 -z 0" />
      <arg name="robot_name"  value="Robot2" />
    </include>
  </group>
</launch>

Move_base launch:

<launch>    
  <!--- Run AMCL -->
  <include file="$(find amcl)/examples/amcl_diff.launch" />

  <!-- Define your move_base node -->
  <node pkg="move_base" type="move_base" respawn="false" name="move_base" output="screen">
    <rosparam file="$(find robot_description)/src/costmap_common_params.yaml" command="load" ns="global_costmap"/>
    <rosparam file="$(find robot_description)/src/costmap_common_params.yaml" command="load" ns="local_costmap" />
    <rosparam file="$(find robot_description)/src/local_costmap_params.yaml"  command="load" />
    <rosparam file="$(find robot_description)/src/global_costmap_params.yaml" command="load" />
    <rosparam file="$(find robot_description)/src/base_local_planner_params.yaml" command="load" />

  <remap from="map" to="/map" />
  </node>
</launch>

Edit 2: Tf frames:

rqt_graph: